JW2A.32.pdf OFC/NFOEC Technical Digest © 2013 OSA Detailed experimental phase noise characterization of Y-branch lasers for use in coherent communication systems Regan T. Watts 1 , Kai Shi 1 , Yonglin Yu 2 , and Liam P. Barry 1 1 The Rince Institute, School of Electronic Engineering, Dublin City University, Glasnevin, Dublin 9, Ireland 2 Wuhan National Laboratory for Optoelectronics, College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, China Author e-mail address: regan.watts@dcu.ie Abstract: We demonstrate for the first time a detailed phase noise characterization of Y-branch lasers. BER tests of 10.7GBaud DQPSK revealed the effect of phase noise at frequencies around the relaxation oscillation peak on system performance. OCIS codes: (250.5960) Semiconductor lasers; (060.1660) Coherent communications 1. Introduction The rise of rapidly reconfigurable, wavelength-flexible or bandwidth-flexible optical networks, such as burst mode or packet switched networks [1] continues to be enabled through to the development of rapidly-tunable semiconductor lasers. With the emergence of coherent receivers, these rapidly-tunable lasers are now employed as flexible local oscillators, in applications such as coherent packet switched systems [2]. Laser phase noise characterization of these lasers is becoming increasingly important, especially for widely-tunable multi-section lasers which suffer from significant 1/f noise from the passive sections [3]. In the presence of considerable 1/f noise, the conventional delayed-self heterodyne measurement technique fails to accurately determine the optical linewidth, however new techniques have been proposed to unambiguously characterize the different contributions to the laser phase noise (1/f and white noise), typically by performing FM-noise spectrum measurements [4, 5]. However, the techniques above have only been used to characterize a few operating points of widely-tunable lasers, such as sampled grating distributed Bragg reflector (SG-DBR) and digital supermode DBR (DS-DBR) structures, which do not provide sufficient information regarding the calibration of the widely-tunable multi-section lasers for use in coherent communication systems. In this work, for the first time to our knowledge, we present a detailed experimental characterization of the laser phase noise of the modulated grating Y-branch (MGY) laser structure with a grid consisting of 4356 operating points (66  66 grid) using FM-noise spectrum measurements. The MGY laser is also employed in a 10.7GBaud differential quadrature-phase shift keyed (DQPSK) modulation experiment looking at bit error rate (BER) performance for different operating points of the laser. The BER performance is then related to the FM-noise spectra and relative intensity noise (RIN) measurements of these laser sources. 2. Laser phase noise characterization of MGY laser Detailed phase noise characterizations were conducted on two separate MGY ILTA modules (Finisar S7610) to ensure a level of consistency in performance. Both lasers performed similarly for all measurements outlined in the follow sections, but the results for just one of the laser modules are shown here. Fig. 1 (a) shows the SMSR tuning map for MGY laser (the grid consists of 66  66 operating points; 8-16mA on the left section current, 11-18mA on the right section current) and shows that the SMSR is at its highest towards the bottom-center of each of the longitudinal modes. The white crosses that run through the center of the supermode depict the 65 operating points that are analyzed in more detail in Fig. 2. The white circles labeled OP1OP4 depict the four operating points that Fig. 1 (a) SMSR tuning map, where white crosses depict the operating points for the tuning curves, and white circles depict the operating points OP1-OP4 for BER measurements, (b) low frequency optical linewidth tuning map, and (c) high frequency optical linewidth tuning map.